1. Field of the Invention
The present invention relates to an Ether transmission system, and more particularly to a high-speed/high-reliability Ether transmission system in a network physical layer and an I/F apparatus.
2. Description of the Related Art
It can be said that an Ether transmission system relating to a network physical layer is a de facto standard in configuring a LAN with the widespread use of the Internet. In other words, it is no exaggeration to say that most of the existing LANs employ the Ether transmission system. This results from an improved performance to cost ratio or the like in the network physical layer by the economies of mass production, and the domination of the Ether transmission system over other transmission systems.
The Ether transmission system comprises terminals such as computers and hubs having functions for reading a MAC (Media Access Control) address of a target in a data frame sent from the terminal and for transferring the data frame only to the terminal corresponding to the address, and the like.
As an access scheme, CSMA/CD (Carrier Sense Multiple Access/Collision Detection) is used. Specifically, while a terminal transmits, the other terminals connected to the same hub as the terminal cannot transmit. Thus, carrier sense is performed such that a check is made to determine whether data is present on a cable, and if no data is present, data is transmitted, thereby enabling multiple access in which accesses of a plurality of users are possible from terminals using a LAN. In addition, since a data leg collision occurs when a plurality of users simultaneously transmit data from respective terminals, an access scheme in which collision detection is performed is employed for retransmitting data individually after a predetermined amount of time.
Because of such features, only two terminals (terminals on transmission and reception) can simultaneously utilize the LAN and the transfer efficiency is not favorable. To eliminate the disadvantage, at present, a switching hub (a switching hub is hereinafter referred to as “hub”) which allows communication among a plurality of pairs of terminals at the same time by dynamically and electrically switching connections among the plurality of terminals connected to the hub at the transmission has been developed and become remarkably popular.
In the Ether transmission system, as the number of terminals connected to the LAN is increased, the concentration of accesses to a file server and the like may cause a situation in which the transmission speed is gradually reduced. On the other hand, improvement in the speed in the network physical layer is always required in connection with advanced techniques for WWW or the like in reality. Specifically, needed is the improvement in the transmission speed between a terminal and a number of terminals and the improvement in the transmission speed between a terminal and a terminal.
To address such needs, for example, prior art (a) and prior art (b) have been proposed. In prior art (a), a higher speed is provided by an approach for radically changing the transmission system in the network physical layer such as the introduction of a gigabit Ether for the 100Base-T. In prior art (b), a higher speed is provided by utilizing a plurality of conventional network physical layers as disclosed in Japanese Patent Laid-open Publication No. 10-336201.
The approach of prior art (a) for providing a higher speed by radically changing the transmission system in the network physical layer is based on the idea of replacing the conventional network physical layer with a faster one. Since a transmission line itself is basically formed of a single line similarly to the conventional system, it is not possible to realize high reliability for faults of the transmission line and the like. In addition, when the network physical layer is replaced with a faster one, the performance thereof is not offered unless network physical layer interfaces at both ends of the transmission line are also replaced with faster ones in any transmission such as one-to-one communication and one-to-multiple communication. Thus, prior art (a) requires a significant initial investment for a higher speed and represents problems in terms of cost.
Next, the approach of prior art (b) for providing a higher speed by utilizing a plurality of network physical layers involves multiple-to-multiple connection or the like over relays, but lacks the contents of address resolution in an Ethernet protocol such as the relationship between an IP address and a MAC (Media Access Control) address, and it is interpreted as a network with its own protocol configured by using hardware of an Ether network between relays, and actually does not constitute an Ether network.
Specifically, in an Ether network, for transferring an Ether frame from a PC to an arbitrary target PC, it is necessary to know the IP address on the application in the target PC, and transfer control is possible only for the MAC address on the operating system (OS) corresponding to the IP address of the target PC at the transfer of a frame. Thus, when only the IP address of the target PC is known, an ARP protocol is used in which a frame for broadcasting a MAC address at frame transfer is sent to acquire a MAC address of a target in an ARP response. In contrast, prior art (b) lacks description of reasonable address resolution for a MAC address of a port, and it is considered as a system for simply recognizing only an opposing target to perform communication. In such a system, the Ether compatibility is not provided over relays, and a connection to a normal Ethernet is not possible and extensibility is poor.
If prior art (b) is applied to a network in which a corresponding relationship is provided between only one IP address possessed by an information processing device and a plurality of MAC addresses for a plurality of ports, it is contemplated that since no limitations are imposed on the MAC addresses, a collision occurs in the ARP protocol for broadcasting a MAC address, an alternative connection protocol to the ARP protocol is not present over relays and the like, and a special protocol in prior art (b) is present. In any case, a physical layer is realized without compatibility with the Ether transmission system.
Thus, prior art (b) is not necessarily an Ether transmission system but an approach which allows replacement with a prior art transmission system such as serial transmission, and realizes a network physical layer without compatibility with the Ether transmission system. In addition, since prior art (b) does not implement the ARP protocol, it has the problem of the inability to extend a network with the Ether transmission system by connecting another terminal between relays and the like.